Recently, it has been predicted that fossil fuels will be depleted in future. In order to solve energy problems, it is an urgent issue to establish technologies for producing next-generation energy alterative to fossil fuels. As one of them, a technology for biofuel production using photosynthetic organisms such as cyanobacteria and algae has attracted attention and been researched. The photosynthetic organisms can produce biofuels from carbon, which was photosynthetically fixed from CO2 and water using light as an energy source. In addition, the photosynthetic organisms are not competitive with food raw materials and can realize carbon-neutral fuel production. Because of these advantages, the photosynthetic organisms are expected as a next-generation energy production system.
Cyanobacteria (also called blue-green algae) belong to a group of eubacteria and have an ability to fix CO2 and produce oxygen through photosynthesis. Cyanobacteria, which have an outer membrane and a cell wall formed of peptidoglycan, fall into the category of gram-negative bacteria but are phylogenetically far from typical gram-negative bacteria. Over a billion years ago, cyanobacteria were engulfed by eukaryotic cells. Such intracellular symbiont (primary symbiosis), cyanobacteria, are considered as an origin of chloroplasts and thus have been widely used in photosynthesis studies as an ancestor organism of chloroplasts.
Cyanobacteria grow fast and have a high photosynthetic ability as well as a transformation ability. Because of this, cyanobacterial cells, to which foreign DNA is introduced, can be used in microbiological production of substances and thus have attracted attention as a microbial host for producing a biofuel. As examples of biofuels produced by cyanobacteria, hydrogen (Non Patent Literature 1), ethanol (Non Patent Literature 2), isobutanol (Non Patent Literature 3) and fatty acids (Non Patent Literature 4) are reported. Non Patent Literature 4 and Patent Literature 1 describe a method for converting inorganic carbon to a fatty acid by culturing a recombinant cyanobacterial cell producing exogenic acyl-ACP thioesterase.    (Patent Literature 1) JP-A-2011-505838    (Non Patent Literature 1) Yoshino F. et al. (2007) Mar. Biotechnol. 9: 101-112    (Non Patent Literature 2) Deng M. D. and Coleman J. R. (1999) Appl. Environ. Microbiol. 65: 523-528    (Non Patent Literature 3) Atsumi S. et al. (2009) Nat. Biotechnol. 27: 1177-1180    (Non Patent Literature 4) Liu X. et al. (2011) Proc. Natl. Acad. Sci. USA. 108: 6899-6904